const EARTH_RADIUS = 6378137.0;    //单位M
const PI = Math.PI;

const getRad = (d) => {
	return d*PI/180.0;
}
//获取经纬度距(米)

// 方式1
export const getGreatCircleDistance = (point1,point2) => {
	let [lat1, lng1] = point1;
	let [lat2, lng2] = point2;
	var radLat1 = getRad(lat1);
	var radLat2 = getRad(lat2);
	
	var a = radLat1 - radLat2;
	var b = getRad(lng1) - getRad(lng2);
	
	var s = 2*Math.asin(Math.sqrt(Math.pow(Math.sin(a/2),2) + Math.cos(radLat1)*Math.cos(radLat2)*Math.pow(Math.sin(b/2),2)));
	s = s*EARTH_RADIUS;
	s = Math.round(s*10000)/10000.0;
			
	return s;
}
// 方式2  地球是椭圆形的计算公式
export const getFlatternDistance2 = (point1,point2) => {
	let [lat1, lng1] = point1;
	let [lat2, lng2] = point2;
	var f = getRad((lat1 + lat2)/2);
	var g = getRad((lat1 - lat2)/2);
	var l = getRad((lng1 - lng2)/2);
	
	var sg = Math.sin(g);
	var sl = Math.sin(l);
	var sf = Math.sin(f);
	
	var s,c,w,r,d,h1,h2;
	var a = EARTH_RADIUS;
	var fl = 1/298.257;
	
	sg = sg*sg;
	sl = sl*sl;
	sf = sf*sf;
	
	s = sg*(1-sl) + (1-sf)*sl;
	c = (1-sg)*(1-sl) + sf*sl;
	
	w = Math.atan(Math.sqrt(s/c));
	r = Math.sqrt(s*c)/w;
	d = 2*w*a;
	h1 = (3*r -1)/2/c;
	h2 = (3*r +1)/2/s;
	
	return d*(1 + fl*(h1*sf*(1-sg) - h2*(1-sf)*sg));
}